Media - Oriented Rate Selection Algorithm for IEEE 802.11 WLANs

Current wireless LANs treat multimedia flows and classical data flows alike. Typically, the same error control mechanisms are used for video flows, which are generally error tolerant but delay sensitive, and TCP flows which are error-intolerant and delay insensitive. The performance of multimedia applications can be significantly improved by some degree of cross-layer awareness. In this paper, we focus on the optimization of real-time multimedia transmission over 802.11-based wireless networks. In particular, we propose a simple and efficient cross-layer mechanism for dynamically selecting the transmission mode that considers both the channel conditions and characteristics of the media. This mechanism called media-oriented rate selection algorithm (MORSA) targets loss-tolerant applications such as audio/video conferencing or VoD that do not require full reliable transmission. We provide an evaluation of this mechanism for MANETs using simulations with NS-2 and analyze the video quality obtained with a fine-grain scalable video encoder based on a motion-compensated spatio temporal wavelet transform. Our results show that the proposed cross-layer approach achieves up to 4 Mbps increase in throughput and that the routing overhead decreases significantly. The transmission of a sample video flow over an 802.11a wireless channel has been evaluated with MORSA and compared with the traditional approach. Significant improvement is observed in throughput, latency, and jitter while keeping a good level of video quality.